Replace WebDatabaseObserver with callbacks

TBR=tim@chromium.org (sync/glue changes)
BUG=230920

Review URL: https://chromiumcodereview.appspot.com/15927029

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@204894 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 128 insertions, 141 deletions

diff --git a/chrome/browser/sync/glue/autofill_data_type_controller.cc b/chrome/browser/sync/glue/autofill_data_type_controller.cc
index 20f0c7b..ba5a1be 100644
--- a/chrome/browser/sync/glue/autofill_data_type_controller.cc
+++ b/chrome/browser/sync/glue/autofill_data_type_controller.cc
@@ -40,16 +40,11 @@ void AutofillDataTypeController::WebDatabaseLoaded() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK_EQ(MODEL_STARTING, state());
 
-  if (web_data_service_.get())
-    web_data_service_->RemoveDBObserver(this);
-
   OnModelLoaded();
 }
 
 AutofillDataTypeController::~AutofillDataTypeController() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  if (web_data_service_.get())
-    web_data_service_->RemoveDBObserver(this);
 }
 
 bool AutofillDataTypeController::PostTaskOnBackendThread(
@@ -63,13 +58,17 @@ bool AutofillDataTypeController::StartModels() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK_EQ(MODEL_STARTING, state());
 
-  web_data_service_ =
+  autofill::AutofillWebDataService* web_data_service =
       autofill::AutofillWebDataService::FromBrowserContext(profile());
-  if (web_data_service_->IsDatabaseLoaded()) {
+
+  if (!web_data_service)
+    return false;
+
+  if (web_data_service->IsDatabaseLoaded()) {
     return true;
   } else {
-    if (web_data_service_.get())
-      web_data_service_->AddDBObserver(this);
+    web_data_service->RegisterDBLoadedCallback(base::Bind(
+        &AutofillDataTypeController::WebDatabaseLoaded, this));
     return false;
   }
 }
@@ -78,8 +77,6 @@ void AutofillDataTypeController::StopModels() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(state() == STOPPING || state() == NOT_RUNNING || state() == DISABLED);
   DVLOG(1) << "AutofillDataTypeController::StopModels() : State = " << state();
-  if (web_data_service_.get())
-    web_data_service_->RemoveDBObserver(this);
 }
 
 void AutofillDataTypeController::StartAssociating(
@@ -89,6 +86,8 @@ void AutofillDataTypeController::StartAssociating(
   ProfileSyncService* sync = ProfileSyncServiceFactory::GetForProfile(
       profile());
   DCHECK(sync);
+  scoped_refptr<autofill::AutofillWebDataService> web_data_service =
+      autofill::AutofillWebDataService::FromBrowserContext(profile());
   bool cull_expired_entries = sync->current_experiments().autofill_culling;
   // First, post the update task to the DB thread, which guarantees us it
   // would run before anything StartAssociating does (e.g.
@@ -98,15 +97,17 @@ void AutofillDataTypeController::StartAssociating(
       base::Bind(
           &AutofillDataTypeController::UpdateAutofillCullingSettings,
           this,
-          cull_expired_entries));
+          cull_expired_entries,
+          web_data_service));
   NonUIDataTypeController::StartAssociating(start_callback);
 }
 
 void AutofillDataTypeController::UpdateAutofillCullingSettings(
-    bool cull_expired_entries) {
+    bool cull_expired_entries,
+    scoped_refptr<autofill::AutofillWebDataService> web_data_service) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
   AutocompleteSyncableService* service =
-      AutocompleteSyncableService::FromWebDataService(web_data_service_.get());
+      AutocompleteSyncableService::FromWebDataService(web_data_service);
   if (!service) {
     DVLOG(1) << "Can't update culling, no AutocompleteSyncableService.";
     return;
diff --git a/chrome/browser/sync/glue/autofill_data_type_controller.h b/chrome/browser/sync/glue/autofill_data_type_controller.h
index 7fc275f..bb513d3 100644
--- a/chrome/browser/sync/glue/autofill_data_type_controller.h
+++ b/chrome/browser/sync/glue/autofill_data_type_controller.h
@@ -11,7 +11,6 @@
 #include "base/gtest_prod_util.h"
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/sync/glue/non_ui_data_type_controller.h"
-#include "components/webdata/common/web_database_observer.h"
 
 namespace autofill {
 class AutofillWebDataService;
@@ -21,8 +20,7 @@ namespace browser_sync {
 
 // A class that manages the startup and shutdown of autofill sync.
 class AutofillDataTypeController
-    : public NonUIDataTypeController,
-      public WebDatabaseObserver {
+    : public NonUIDataTypeController {
  public:
   AutofillDataTypeController(
       ProfileSyncComponentsFactory* profile_sync_factory,
@@ -37,9 +35,6 @@ class AutofillDataTypeController
   // 163431 is addressed / implemented.
   virtual void StartAssociating(const StartCallback& start_callback) OVERRIDE;
 
-  // WebDatabaseObserver implementation.
-  virtual void WebDatabaseLoaded() OVERRIDE;
-
  protected:
   virtual ~AutofillDataTypeController();
 
@@ -57,9 +52,11 @@ class AutofillDataTypeController
 
   // Self-invoked on the DB thread to call the AutocompleteSyncableService with
   // an updated value of autofill culling settings.
-  void UpdateAutofillCullingSettings(bool cull_expired_entries);
+  void UpdateAutofillCullingSettings(bool cull_expired_entries,
+      scoped_refptr<autofill::AutofillWebDataService> web_data_service);
 
-  scoped_refptr<autofill::AutofillWebDataService> web_data_service_;
+  // Callback once WebDatabase has loaded.
+  void WebDatabaseLoaded();
 
   DISALLOW_COPY_AND_ASSIGN(AutofillDataTypeController);
 };
diff --git a/chrome/browser/sync/glue/autofill_data_type_controller_unittest.cc b/chrome/browser/sync/glue/autofill_data_type_controller_unittest.cc
index 1f72386..ce020f9 100644
--- a/chrome/browser/sync/glue/autofill_data_type_controller_unittest.cc
+++ b/chrome/browser/sync/glue/autofill_data_type_controller_unittest.cc
@@ -21,7 +21,6 @@
 #include "chrome/test/base/profile_mock.h"
 #include "components/autofill/browser/webdata/autofill_webdata_service.h"
 #include "components/webdata/common/web_data_service_test_util.h"
-#include "components/webdata/common/web_database_observer.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_source.h"
 #include "content/public/browser/notification_types.h"
@@ -61,34 +60,24 @@ class FakeWebDataService : public AutofillWebDataService {
   FakeWebDataService()
       : AutofillWebDataService(),
         is_database_loaded_(false),
-        observer_(NULL) {}
+        db_loaded_callback_(base::Callback<void(void)>()){}
 
   // Mark the database as loaded and send out the appropriate notification.
   void LoadDatabase() {
     StartSyncableService();
     is_database_loaded_ = true;
-    if (observer_)
-      observer_->WebDatabaseLoaded();
+
+    if (!db_loaded_callback_.is_null())
+      db_loaded_callback_.Run();
   }
 
   virtual bool IsDatabaseLoaded() OVERRIDE {
     return is_database_loaded_;
   }
 
-  // Note: this implementation violates the contract for AddDBObserver (which
-  // should support having multiple observers at the same time), however, it
-  // is the simplest thing that works for the purpose of the unit test, which
-  // only registers one observer.
-  virtual void AddDBObserver(WebDatabaseObserver* observer) OVERRIDE {
-    DCHECK(!observer_);
-    observer_ = observer;
-  }
-
-  virtual void RemoveDBObserver(WebDatabaseObserver* observer) OVERRIDE {
-    if (!observer_)
-      return;
-    DCHECK_EQ(observer_, observer);
-    observer_ = NULL;
+  virtual void RegisterDBLoadedCallback(
+      const base::Callback<void(void)>& callback) OVERRIDE {
+    db_loaded_callback_ = callback;
   }
 
   void StartSyncableService() {
@@ -131,7 +120,7 @@ class FakeWebDataService : public AutofillWebDataService {
 
   bool is_database_loaded_;
   NoOpAutofillBackend autofill_backend_;
-  WebDatabaseObserver* observer_;
+  base::Callback<void(void)> db_loaded_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeWebDataService);
 };
diff --git a/chrome/browser/sync/glue/autofill_profile_data_type_controller.cc b/chrome/browser/sync/glue/autofill_profile_data_type_controller.cc
index 479fe764..a480737 100644
--- a/chrome/browser/sync/glue/autofill_profile_data_type_controller.cc
+++ b/chrome/browser/sync/glue/autofill_profile_data_type_controller.cc
@@ -28,7 +28,8 @@ AutofillProfileDataTypeController::AutofillProfileDataTypeController(
     : NonUIDataTypeController(profile_sync_factory,
                               profile,
                               sync_service),
-      personal_data_(NULL) {}
+      personal_data_(NULL),
+      callback_registered_(false) {}
 
 syncer::ModelType AutofillProfileDataTypeController::type() const {
   return syncer::AUTOFILL_PROFILE;
@@ -41,8 +42,6 @@ syncer::ModelSafeGroup
 
 void AutofillProfileDataTypeController::WebDatabaseLoaded() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  if (web_data_service_.get())
-    web_data_service_->RemoveDBObserver(this);
   OnModelLoaded();
 }
 
@@ -51,15 +50,19 @@ void AutofillProfileDataTypeController::OnPersonalDataChanged() {
   DCHECK_EQ(state(), MODEL_STARTING);
 
   personal_data_->RemoveObserver(this);
-  web_data_service_ = AutofillWebDataService::FromBrowserContext(profile());
+  autofill::AutofillWebDataService* web_data_service =
+      autofill::AutofillWebDataService::FromBrowserContext(profile());
 
-  if (!web_data_service_.get())
+  if (!web_data_service)
     return;
 
-  if (web_data_service_->IsDatabaseLoaded())
+  if (web_data_service->IsDatabaseLoaded()) {
     OnModelLoaded();
-  else
-    web_data_service_->AddDBObserver(this);
+  } else  if (!callback_registered_) {
+     web_data_service->RegisterDBLoadedCallback(base::Bind(
+        &AutofillProfileDataTypeController::WebDatabaseLoaded, this));
+     callback_registered_ = true;
+  }
 }
 
 AutofillProfileDataTypeController::~AutofillProfileDataTypeController() {}
@@ -84,15 +87,21 @@ bool AutofillProfileDataTypeController::StartModels() {
     return false;
   }
 
-  web_data_service_ = AutofillWebDataService::FromBrowserContext(profile());
+  autofill::AutofillWebDataService* web_data_service =
+      AutofillWebDataService::FromBrowserContext(profile());
 
-  if (!web_data_service_.get())
+  if (!web_data_service)
     return false;
 
-  if (web_data_service_->IsDatabaseLoaded())
+  if (web_data_service->IsDatabaseLoaded())
     return true;
 
-  web_data_service_->AddDBObserver(this);
+  if (!callback_registered_) {
+     web_data_service->RegisterDBLoadedCallback(base::Bind(
+        &AutofillProfileDataTypeController::WebDatabaseLoaded, this));
+     callback_registered_ = true;
+  }
+
   return false;
 }
 
@@ -100,9 +109,6 @@ void AutofillProfileDataTypeController::StopModels() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(state() == STOPPING || state() == NOT_RUNNING);
 
-  if (web_data_service_.get())
-    web_data_service_->RemoveDBObserver(this);
-
   personal_data_->RemoveObserver(this);
 }
 
diff --git a/chrome/browser/sync/glue/autofill_profile_data_type_controller.h b/chrome/browser/sync/glue/autofill_profile_data_type_controller.h
index d49a2f5..3e00748 100644
--- a/chrome/browser/sync/glue/autofill_profile_data_type_controller.h
+++ b/chrome/browser/sync/glue/autofill_profile_data_type_controller.h
@@ -10,10 +10,8 @@
 #include "base/scoped_observer.h"
 #include "chrome/browser/sync/glue/non_ui_data_type_controller.h"
 #include "components/autofill/browser/personal_data_manager_observer.h"
-#include "components/webdata/common/web_database_observer.h"
 
 namespace autofill {
-class AutofillWebDataService;
 class PersonalDataManager;
 }  // namespace autofill
 
@@ -21,7 +19,6 @@ namespace browser_sync {
 
 class AutofillProfileDataTypeController
     : public NonUIDataTypeController,
-      public WebDatabaseObserver,
       public autofill::PersonalDataManagerObserver {
  public:
   AutofillProfileDataTypeController(
@@ -33,9 +30,6 @@ class AutofillProfileDataTypeController
   virtual syncer::ModelType type() const OVERRIDE;
   virtual syncer::ModelSafeGroup model_safe_group() const OVERRIDE;
 
-  // WebDatabaseObserver implementation.
-  virtual void WebDatabaseLoaded() OVERRIDE;
-
   // PersonalDataManagerObserver implementation:
   virtual void OnPersonalDataChanged() OVERRIDE;
 
@@ -50,8 +44,11 @@ class AutofillProfileDataTypeController
   virtual void StopModels() OVERRIDE;
 
  private:
+  // Callback to notify that WebDatabase has loaded.
+  void WebDatabaseLoaded();
+
   autofill::PersonalDataManager* personal_data_;
-  scoped_refptr<autofill::AutofillWebDataService> web_data_service_;
+  bool callback_registered_;
 
   DISALLOW_COPY_AND_ASSIGN(AutofillProfileDataTypeController);
 };
diff --git a/components/webdata.gypi b/components/webdata.gypi
index d918422..f728c21 100644
--- a/components/webdata.gypi
+++ b/components/webdata.gypi
@@ -54,7 +54,6 @@
       'sources': [
         'webdata/common/web_database.cc',
         'webdata/common/web_database.h',
-        'webdata/common/web_database_observer.h',
         'webdata/common/web_database_service.cc',
         'webdata/common/web_database_service.h',
         'webdata/common/web_database_table.cc',
diff --git a/components/webdata/common/web_data_service_base.cc b/components/webdata/common/web_data_service_base.cc
index 209e612..c00a687 100644
--- a/components/webdata/common/web_data_service_base.cc
+++ b/components/webdata/common/web_data_service_base.cc
@@ -26,7 +26,6 @@ using content::BrowserThread;
 WebDataServiceBase::WebDataServiceBase(scoped_refptr<WebDatabaseService> wdbs,
                                        const ProfileErrorCallback& callback)
     : wdbs_(wdbs),
-      db_loaded_(false),
       profile_error_callback_(callback) {
   // WebDataService requires DB thread if instantiated.
   // Set WebDataServiceFactory::GetInstance()->SetTestingFactory(&profile, NULL)
@@ -34,22 +33,12 @@ WebDataServiceBase::WebDataServiceBase(scoped_refptr<WebDatabaseService> wdbs,
   DCHECK(BrowserThread::IsWellKnownThread(BrowserThread::DB));
 }
 
-void WebDataServiceBase::WebDatabaseLoaded() {
-  db_loaded_ = true;
-}
-
-void WebDataServiceBase::WebDatabaseLoadFailed(sql::InitStatus status) {
-  if (!profile_error_callback_.is_null())
-    profile_error_callback_.Run(status);
-}
-
 void WebDataServiceBase::ShutdownOnUIThread() {
-  db_loaded_ = false;
 }
 
 void WebDataServiceBase::Init() {
   DCHECK(wdbs_.get());
-  wdbs_->AddObserver(this);
+  wdbs_->RegisterDBErrorCallback(profile_error_callback_);
   wdbs_->LoadDatabase();
 }
 
@@ -76,19 +65,16 @@ content::NotificationSource WebDataServiceBase::GetNotificationSource() {
 }
 
 bool WebDataServiceBase::IsDatabaseLoaded() {
-  return db_loaded_;
+  if (!wdbs_)
+    return false;
+  return wdbs_->db_loaded();
 }
 
-void WebDataServiceBase::AddDBObserver(WebDatabaseObserver* observer) {
-  if (!wdbs_.get())
-    return;
-  wdbs_->AddObserver(observer);
-}
-
-void WebDataServiceBase::RemoveDBObserver(WebDatabaseObserver* observer) {
-  if (!wdbs_.get())
+void WebDataServiceBase::RegisterDBLoadedCallback(
+    const base::Callback<void(void)>& callback) {
+  if (!wdbs_)
     return;
-  wdbs_->RemoveObserver(observer);
+  wdbs_->RegisterDBLoadedCallback(callback);
 }
 
 WebDatabase* WebDataServiceBase::GetDatabase() {
diff --git a/components/webdata/common/web_data_service_base.h b/components/webdata/common/web_data_service_base.h
index 9e0867d..11d5d3e 100644
--- a/components/webdata/common/web_data_service_base.h
+++ b/components/webdata/common/web_data_service_base.h
@@ -9,7 +9,6 @@
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "components/webdata/common/web_database_observer.h"
 #include "components/webdata/common/webdata_export.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_source.h"
@@ -25,8 +24,7 @@ class Thread;
 
 // Base for WebDataService class hierarchy.
 class WEBDATA_EXPORT WebDataServiceBase
-    : public WebDatabaseObserver,
-      public base::RefCountedThreadSafe<WebDataServiceBase,
+    : public base::RefCountedThreadSafe<WebDataServiceBase,
           content::BrowserThread::DeleteOnUIThread> {
  public:
   // All requests return an opaque handle of the following type.
@@ -50,10 +48,6 @@ class WEBDATA_EXPORT WebDataServiceBase
   WebDataServiceBase(scoped_refptr<WebDatabaseService> wdbs,
                      const ProfileErrorCallback& callback);
 
-  // WebDatabaseObserver implementation.
-  virtual void WebDatabaseLoaded() OVERRIDE;
-  virtual void WebDatabaseLoadFailed(sql::InitStatus status) OVERRIDE;
-
   // Cancel any pending request. You need to call this method if your
   // WebDataServiceConsumer is about to be deleted.
   virtual void CancelRequest(Handle h);
@@ -76,8 +70,13 @@ class WEBDATA_EXPORT WebDataServiceBase
   // Unloads the database permanently and shuts down service.
   void ShutdownDatabase();
 
-  virtual void AddDBObserver(WebDatabaseObserver* observer);
-  virtual void RemoveDBObserver(WebDatabaseObserver* observer);
+  // Register a callback to be notified that the database has loaded. Multiple
+  // callbacks may be registered, and each will be called at most once
+  // (following a successful database load), then cleared.
+  // Note: if the database load is already complete, then the callback will NOT
+  // be stored or called.
+  virtual void RegisterDBLoadedCallback(
+      const base::Callback<void(void)>& callback);
 
   // Returns true if the database load has completetd successfully, and
   // ShutdownOnUIThread has not yet been called.
@@ -94,9 +93,6 @@ class WEBDATA_EXPORT WebDataServiceBase
   // Our database service.
   scoped_refptr<WebDatabaseService> wdbs_;
 
-  // True if we've received a notification that the WebDatabase has loaded.
-  bool db_loaded_;
-
  private:
   friend struct content::BrowserThread::DeleteOnThread<
       content::BrowserThread::UI>;
diff --git a/components/webdata/common/web_database_observer.h b/components/webdata/common/web_database_observer.h
deleted file mode 100644
index 5ea8002..0000000
--- a/components/webdata/common/web_database_observer.h
+++ /dev/null
@@ -1,26 +0,0 @@
-// Copyright (c) 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef COMPONENTS_WEBDATA_COMMON_WEB_DATABASE_OBSERVER_H_
-#define COMPONENTS_WEBDATA_COMMON_WEB_DATABASE_OBSERVER_H_
-
-#include "components/webdata/common/webdata_export.h"
-#include "sql/init_status.h"
-
-// WebDatabase loads asynchronously on the DB thread. Clients on the UI thread
-// can use this interface to be notified when the load is complete, or if it
-// fails.
-class WEBDATA_EXPORT WebDatabaseObserver {
- public:
-  // Called when DB has been loaded successfully.
-  virtual void WebDatabaseLoaded() = 0;
-  // Called when load failed. |status| contains error code.
-  virtual void WebDatabaseLoadFailed(sql::InitStatus status) {};
-
- protected:
-  virtual ~WebDatabaseObserver() {}
-};
-
-
-#endif  // COMPONENTS_WEBDATA_COMMON_WEB_DATABASE_OBSERVER_H_
diff --git a/components/webdata/common/web_database_service.cc b/components/webdata/common/web_database_service.cc
index a1b1889..88a7c89 100644
--- a/components/webdata/common/web_database_service.cc
+++ b/components/webdata/common/web_database_service.cc
@@ -40,7 +40,8 @@ class WebDatabaseService::BackendDelegate :
 WebDatabaseService::WebDatabaseService(
     const base::FilePath& path)
     : path_(path),
-      weak_ptr_factory_(this) {
+      weak_ptr_factory_(this),
+      db_loaded_(false) {
   // WebDatabaseService should be instantiated on UI thread.
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   // WebDatabaseService requires DB thread if instantiated.
@@ -68,6 +69,7 @@ void WebDatabaseService::LoadDatabase() {
 }
 
 void WebDatabaseService::UnloadDatabase() {
+  db_loaded_ = false;
   if (!wds_backend_.get())
     return;
   BrowserThread::PostTask(BrowserThread::DB, FROM_HERE,
@@ -76,9 +78,12 @@ void WebDatabaseService::UnloadDatabase() {
 }
 
 void WebDatabaseService::ShutdownDatabase() {
+  db_loaded_ = false;
+  weak_ptr_factory_.InvalidateWeakPtrs();
+  loaded_callbacks_.clear();
+  error_callbacks_.clear();
   if (!wds_backend_.get())
     return;
-  weak_ptr_factory_.InvalidateWeakPtrs();
   BrowserThread::PostTask(BrowserThread::DB, FROM_HERE,
       Bind(&WebDataServiceBackend::ShutdownDatabase,
            wds_backend_, false));
@@ -140,24 +145,33 @@ void WebDatabaseService::CancelRequest(WebDataServiceBase::Handle h) {
   wds_backend_->request_manager()->CancelRequest(h);
 }
 
-void WebDatabaseService::AddObserver(WebDatabaseObserver* observer) {
-  observer_list_.AddObserver(observer);
+void WebDatabaseService::RegisterDBLoadedCallback(
+    const base::Callback<void(void)>& callback) {
+  loaded_callbacks_.push_back(callback);
 }
 
-void WebDatabaseService::RemoveObserver(WebDatabaseObserver* observer) {
-  observer_list_.RemoveObserver(observer);
+void WebDatabaseService::RegisterDBErrorCallback(
+    const base::Callback<void(sql::InitStatus)>& callback) {
+  error_callbacks_.push_back(callback);
 }
 
 void WebDatabaseService::OnDatabaseLoadDone(sql::InitStatus status) {
   if (status == sql::INIT_OK) {
-    // Notify that the database has been initialized.
-    FOR_EACH_OBSERVER(WebDatabaseObserver,
-                      observer_list_,
-                      WebDatabaseLoaded());
+    db_loaded_ = true;
+
+    for (size_t i = 0; i < loaded_callbacks_.size(); i++) {
+      if (!loaded_callbacks_[i].is_null())
+        loaded_callbacks_[i].Run();
+    }
+
+    loaded_callbacks_.clear();
   } else {
     // Notify that the database load failed.
-    FOR_EACH_OBSERVER(WebDatabaseObserver,
-                      observer_list_,
-                      WebDatabaseLoadFailed(status));
+    for (size_t i = 0; i < error_callbacks_.size(); i++) {
+      if (!error_callbacks_[i].is_null())
+        error_callbacks_[i].Run(status);
+    }
+
+    error_callbacks_.clear();
   }
 }
diff --git a/components/webdata/common/web_database_service.h b/components/webdata/common/web_database_service.h
index cd3ceae..67e95e7 100644
--- a/components/webdata/common/web_database_service.h
+++ b/components/webdata/common/web_database_service.h
@@ -93,8 +93,22 @@ class WEBDATA_EXPORT WebDatabaseService
   // somewhere else.
   virtual void CancelRequest(WebDataServiceBase::Handle h);
 
-  void AddObserver(WebDatabaseObserver* observer);
-  void RemoveObserver(WebDatabaseObserver* observer);
+  // Register a callback to be notified that the database has loaded. Multiple
+  // callbacks may be registered, and each will be called at most once
+  // (following a successful database load), then cleared.
+  // Note: if the database load is already complete, then the callback will NOT
+  // be stored or called.
+  void RegisterDBLoadedCallback(const base::Callback<void(void)>& callback);
+
+  // Register a callback to be notified that the database has failed to load.
+  // Multiple callbacks may be registered, and each will be called at most once
+  // (following a database load failure), then cleared.
+  // Note: if the database load is already complete, then the callback will NOT
+  // be stored or called.
+  void RegisterDBErrorCallback(
+      const base::Callback<void(sql::InitStatus)>& callback);
+
+  bool db_loaded() { return db_loaded_; };
 
  private:
   class BackendDelegate;
@@ -116,10 +130,24 @@ class WEBDATA_EXPORT WebDatabaseService
   // PostTask on DB thread may outlive us.
   scoped_refptr<WebDataServiceBackend> wds_backend_;
 
-  ObserverList<WebDatabaseObserver> observer_list_;
-
   // All vended weak pointers are invalidated in ShutdownDatabase().
   base::WeakPtrFactory<WebDatabaseService> weak_ptr_factory_;
+
+  // Types for managing DB loading callbacks.
+  typedef base::Callback<void(void)> DBLoadedCallback;
+  typedef std::vector<DBLoadedCallback> LoadedCallbacks;
+
+  typedef base::Callback<void(sql::InitStatus)> DBLoadErrorCallback;
+  typedef std::vector<DBLoadErrorCallback> ErrorCallbacks;
+
+  // Callbacks to be called once the DB has loaded.
+  LoadedCallbacks loaded_callbacks_;
+
+  // Callbacks to be called if the DB has failed to load.
+  ErrorCallbacks error_callbacks_;
+
+  // True if the WebDatabase has loaded.
+  bool db_loaded_;
 };
 
 #endif  // COMPONENTS_WEBDATA_COMMON_WEB_DATABASE_SERVICE_H_